1. Field of the Invention
The present invention relates to an apparatus for converting gas using gliding plasma, and more particularly, to an apparatus for converting material gas into desired gas by swirling gliding plasma arc.
2. Description of the Related Art
Various gas conversion apparatuses use plasma to change the molecular structure of gas (material gas) for converting the material gas into a different type of gas (post-reaction gas). Most of the gas conversion apparatuses have a similar structure and operate in a similar manner. That is, most of the gas conversion apparatuses have a mechanism for generating plasma in a closed reaction chamber and injecting material gas into the plasma to collide the molecules of the material gas with the electrons of the plasma for separating molecules of the material gas.
For example, methane, a main component of natural gas, can be converted into acetylene using the gas conversion apparatus. That is, acetylene can be produced from natural gas. As is well-known, the acetylene is a chemical intermediate that can be used in various fields as a starting material for various polymers such as a chlorinated vinyl monomer required for synthetic rubber, acetic acid, vinyl, or PVC.
The acetylene can be produced from the natural gas (specifically, methane) by a high temperature method (thermal treating method) or a low temperature method (non-thermal treating method).
Representative examples of the thermal treating method are an electric arc method and a partial oxidation method.
In the electric arc method, the natural gas is heated to a high temperature using the thermal energy of hot plasma to induce thermo-chemical reaction for obtaining acetylene from the natural gas. German Huel Company's commercial process can be taken as an example of the electric arc method.
In the partial oxidation method, 75% of reaction gas (methane) is burned to generate thermal energy, and then the thermal energy is applied to the remaining 25% of the methane to obtain acetylene by thermo-chemical reaction. BASF Company's partial oxidation combustion process can be taken as a representative example.
However, in producing the acetylene using the thermal treating method, the thermo-chemical reaction is performed at a temperature higher than above 3000K, and worse the thermo-chemical reaction further progresses after the acetylene is already produced to yield carbon and hydrogen from the acetylene. Therefore, the produced acetylene gas must be rapidly quenched to stop the reaction. However, as is well-known, it is difficult to rapidly quench the acetylene gas since gas has a low thermal capacity.
As described above, since the thermal treating method includes an extremely hot reaction process, it is difficult to select suitable materials for a reaction chamber and stop the decomposition reaction. Further, the conversion rate from the natural gas into the acetylene is not so high. Therefore, the non-thermal treating method has been introduced.
A representative example of the non-thermal treating method is a method using non-equilibrium plasma (low-temperature plasma). When methane gas is introduced into the low-temperature plasma, the molecules of the methane collide with electrons having a high energy of the low-temperature plasma, and thereby hydrogen atom is separated from the methane molecules to yield radicals such as methyl (CH3) and methylene (CH2).
The radicals may become ethane (C2H6) by recombining reaction. When energy is continuously applied, the methyl radical (CH3) may become methylene (CH2) or methylidyne (CH) radical by successive dehydrogenation. The CHx radicals obtained as described above make up C2 hydrocarbon such as ethane, ethylene, and acetylene through a recombination process.
FIG. 1 shows a conventional gas conversion apparatus 11 using the gliding plasma, a kind of non-thermal treating method.
Referring to FIG. 1, the conventional gas conversion apparatus 11 includes a reaction chamber 13 providing a closed inner space and having a discharge hole 17 on a lower portion, anode and cathode plates 23 and 25 fixedly installed in the reaction chamber 13, and a power source 19 supplying positive and negative currents to the anode and cathode plates 23 and 25 through power lines 21.
The reaction chamber 13 includes a nozzle 15 in a top plate 13. The nozzle 15 injects gas (hereinafter, referred to as material gas) into the reaction chamber 13 between the anode plate 23 and the cathode plate 25 for converting the material gas.
The anode plate23 and the cathode plate 25 have a blade shape with a constant thickness and vertically fixed by separate supports (not shown). Specifically, the anode plate 23 and the cathode plate 25 face each other, and the facing surfaces of the anode plate 23 and the cathode plate 25 are curved so as to depart from each other further more as they go downward.
When an electricity is applied to the fixed anode and cathode plates 23 and 25, plasma is induced between the fixed anode and cathode plates 23 and 25. The plasma is a gliding plasma (or non-thermal plasma or low-temperature plasma) that glides downward when a downward force is applied by flow of material gas (G). The plasma is placed between the facing surfaces of the anode and cathode plates 23 and 25.
However, the gas conversion rate of the conventional gas conversion apparatus 11 is not good since the plasma region (A) is not sufficient. That is, since the region (A) occupied by the induced plasma is very small when compared with the total space inside the reaction chamber 13, a large portion of the material gas (G) injected into the reaction chamber 13 is not contacted with the plasma before the material gas (G) is discharged through the discharge hole 17, thereby decreasing the gas conversion performance of the gas conversion apparatus 11.
Further, since the plasma region (A) is narrow as described above, the material gas (G) injected from the nozzle 15 passes through the plasma region (A) in a very short time. To solve these problems, that is, to increase the time in which the material gas (G) passes through the plasma region (A), the injection amount of the material gas (G) or the injection speed of the material gas (G) is controlled. However, the gas conversion rate of the gas conversion apparatus is hardly increased by this control.
Referring to a thesis published about the gas conversion apparatus 11, a maximal gas conversion rate of 40% is obtained by maximizing the plasma region (A) and optimally controlling the gas injection amount and the gas injection speed. In this case, 60% of the material gas (G) is discharged to the outside through the discharge hole 17 without reaction with the plasma.
Furthermore, it is very difficult to control the gas conversion rate of the gas conversion apparatus 11. Practically, the gas conversion rate should be increased or decreased according to the kind of desired final object (converted gas). However, since the gas conversion rate of the gas conversion apparatus 11 is controlled by adjusting the injection amount or injection speed of the material gas, the sensitivity of the controlling is not good and the span of control is narrow, thereby precise controlling cannot be attained.